Java 中的栈 peek()方法
java 中的 java.util.Stack.peek()方法用于检索或获取堆栈的第一个元素或堆栈顶部的元素。检索到的元素不会被删除或从堆栈中移除。
语法:
STACK.peek()
参数:该方法不取任何参数。
返回值:该方法返回堆栈顶部的元素，否则如果堆栈为空，则返回空。
异常:如果堆栈为空，该方法抛出 EmptyStackException 。
下面的程序说明了 java.util.Stack.peek()方法: 程序 1:
// Java code to illustrate peek() function
import java.util.*;
public class StackDemo {
public static void main(String args[])
{
// Creating an empty Stack
Stack<String> STACK = new Stack<String>();
// Use push() to add elements into the Stack
STACK.push("Welcome");
STACK.push("To");
STACK.push("Geeks");
STACK.push("For");
STACK.push("Geeks");
// Displaying the Stack
System.out.println("Initial Stack: " + STACK);
// Fetching the element at the head of the Stack
System.out.println("The element at the top of the"
+ " stack is: " + STACK.peek());
// Displaying the Stack after the Operation
System.out.println("Final Stack: " + STACK);
}
}
Output:
Initial Stack: [Welcome, To, Geeks, For, Geeks]
The element at the top of the stack is: Geeks
Final Stack: [Welcome, To, Geeks, For, Geeks]
程序 2:
// Java code to illustrate peek() function
import java.util.*;
public class StackDemo {
public static void main(String args[])
{
// Creating an empty Stack
Stack<Integer> STACK = new Stack<Integer>();
// Use push() to add elements into the Stack
STACK.push(10);
STACK.push(15);
STACK.push(30);
STACK.push(20);
STACK.push(5);
// Displaying the Stack
System.out.println("Initial Stack: " + STACK);
// Fetching the element at the head of the Stack
System.out.println("The element at the top of the"
+ " stack is: " + STACK.peek());
// Displaying the Stack after the Operation
System.out.println("Final Stack: " + STACK);
}
}
Output:
Initial Stack: [10, 15, 30, 20, 5]
The element at the top of the stack is: 5
Final Stack: [10, 15, 30, 20, 5]
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